QFileSystemEngine/Unix: use copy_file_range(2) in cloneFile()

For remote filesystems on Linux, this can invoke a server-side copy to
avoid network traffic. For local filesystems, Linux can use an optimized
FS-specific call (which may be the same operation as the FICLONE, but
I'm not sure) or splice the data on its own.

Tested with:
 - FreeBSD ufs
 - FreeBSD ufs-to-tmpfs
 - FreeBSD tmpfs (tested ENOSPC with it)
 - Linux btrfs
 - Linux ext4
 - Linux tmpfs (tested ENOSPC with it)

Change-Id: I3ae11d555882bdbb0487fffd81cb5568171cee3f
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>

src/corelib/configure.cmake

@@ -143,6 +143,19 @@ int pipes[2];
 }
 ")
 
+# copy_file_range
+qt_config_compile_test(copy_file_range
+    LABEL "copy_file_range()"
+    CODE
+"#include <unistd.h>
+
+int main()
+{
+    off_t off_in = 0, off_out = 1024;
+    return copy_file_range(0, &off_in, 1, &off_out, 2147483647, 0) != 0;
+}
+")
+
 # Check if __cxa_thread_atexit{,_impl} are present in the C library (hence why
 # PROJECT_PATH instead of CODE for C++). Either one suffices to disable
 # FEATURE_broken_threadlocal_dtors. See details in qthread_unix.cpp.
@@ -615,6 +628,11 @@ qt_feature("close_range" PRIVATE
     CONDITION QT_FEATURE_process AND TEST_close_range
     AUTODETECT UNIX
 )
+qt_feature("copy_file_range" PRIVATE
+    LABEL "copy_file_range()"
+    CONDITION QT_FEATURE_process AND TEST_copy_file_range
+    AUTODETECT UNIX AND NOT DARWIN
+)
 qt_feature("doubleconversion" PRIVATE
     LABEL "DoubleConversion"
 )

src/corelib/global/minimum-linux_p.h

@@ -41,6 +41,7 @@ QT_BEGIN_NAMESPACE
  * - accept4                    2.6.28
  * - renameat2                  3.16                    QT_CONFIG(renameat2)
  * - getrandom                  3.17                    QT_CONFIG(getentropy)
+ * - copy_file_range            4.5                     QT_CONFIG(copy_file_range)
  * - statx                      4.11                    STATX_BASIC_STATS
  */
 
@@ -50,6 +51,10 @@ QT_BEGIN_NAMESPACE
 #  define QT_ELF_NOTE_OS_MAJOR      4
 #  define QT_ELF_NOTE_OS_MINOR      11
 #  define QT_ELF_NOTE_OS_PATCH      0
+#elif QT_CONFIG(copy_file_range)
+#  define QT_ELF_NOTE_OS_MAJOR      4
+#  define QT_ELF_NOTE_OS_MINOR      5
+#  define QT_ELF_NOTE_OS_PATCH      0
 #elif QT_CONFIG(getentropy)
 #  define QT_ELF_NOTE_OS_MAJOR      3
 #  define QT_ELF_NOTE_OS_MINOR      17
@@ -59,7 +64,6 @@ QT_BEGIN_NAMESPACE
 #  define QT_ELF_NOTE_OS_MINOR      16
 #  define QT_ELF_NOTE_OS_PATCH      0
 #else
-
 #  define QT_ELF_NOTE_OS_MAJOR      2
 #  define QT_ELF_NOTE_OS_MINOR      6
 #  define QT_ELF_NOTE_OS_PATCH      28

src/corelib/global/qconfig-bootstrapped.h

@@ -47,6 +47,7 @@
 #define QT_FEATURE_cborstreamwriter 1
 #define QT_FEATURE_commandlineparser 1
 #define QT_NO_COMPRESS
+#define QT_FEATURE_copy_file_range -1
 #define QT_FEATURE_cxx17_filesystem -1
 #define QT_NO_DATASTREAM
 #define QT_FEATURE_datestring 1

src/corelib/io/qfilesystemengine_unix.cpp

@@ -1096,8 +1096,41 @@ auto QFileSystemEngine::cloneFile(int srcfd, int dstfd, const QFileSystemMetaDat
     // first, try FICLONE (only works on regular files and only on certain fs)
     if (::ioctl(dstfd, FICLONE, srcfd) == 0)
         return TriStateResult::Success;
+#elif defined(Q_OS_DARWIN)
+    // try fcopyfile
+    if (fcopyfile(srcfd, dstfd, nullptr, COPYFILE_DATA | COPYFILE_STAT) == 0)
+        return TriStateResult::Success;
+    switch (errno) {
+    case ENOTSUP:
+    case ENOMEM:
+        return TriStateResult::NotSupported;    // let QFile try
+    }
+    return TriStateResult::Failed;
+#endif
 
-    // Second, try sendfile (it can send to some special types too).
+#if QT_CONFIG(copy_file_range)
+    // Second, try copy_file_range. Tested on Linux & FreeBSD: FreeBSD can copy
+    // across mountpoints, Linux currently (6.12) can only if the source and
+    // destination mountpoints are the same filesystem type.
+    QT_OFF_T srcoffset = 0;
+    QT_OFF_T dstoffset = 0;
+    ssize_t copied;
+    do {
+        copied = ::copy_file_range(srcfd, &srcoffset, dstfd, &dstoffset, SSIZE_MAX, 0);
+    } while (copied > 0 || (copied < 0 && errno == EINTR));
+    if (copied == 0)
+        return TriStateResult::Success;         // EOF -> success
+    if (srcoffset) {
+        // some bytes were copied, so this is a real error (like ENOSPC).
+        copied = ftruncate(dstfd, 0);
+        return TriStateResult::Failed;
+    }
+    if (errno != EXDEV)
+        return TriStateResult::Failed;
+#endif
+
+#if defined(Q_OS_LINUX)
+    // For Linux, try sendfile (it can send to some special types too).
     // sendfile(2) is limited in the kernel to 2G - 4k
     const size_t SendfileSize = 0x7ffff000;
 
@@ -1125,16 +1158,6 @@ auto QFileSystemEngine::cloneFile(int srcfd, int dstfd, const QFileSystemMetaDat
     }
 
     return TriStateResult::Success;
-#elif defined(Q_OS_DARWIN)
-    // try fcopyfile
-    if (fcopyfile(srcfd, dstfd, nullptr, COPYFILE_DATA | COPYFILE_STAT) == 0)
-        return TriStateResult::Success;
-    switch (errno) {
-    case ENOTSUP:
-    case ENOMEM:
-        return TriStateResult::NotSupported;    // let QFile try
-    }
-    return TriStateResult::Failed;
 #else
     Q_UNUSED(dstfd);
     return TriStateResult::NotSupported;